1. Field of the Invention
The present invention relates to a method and an apparatus for enhancing signals, and more particularly to a method and an apparatus for enhancing signals in magnetic resonance imaging (MRI).
2. Background of the Invention
A magnetic resonance imaging (MRI) apparatus is configured to reconstruct MR images based on MR signals. An MRI apparatus typically applies a static magnetic field, a gradient magnetic field, and a radio frequency (RF) signal having a selected frequency to a subject to excite a selected nucleus type and then detects the MR signals responsively sent by the excited nucleus.
Referring to FIG. 1, in a conventional procedure of 2D spatial encoding, only one single slice of the subject can be processed at a time; that is, multi-slice images are acquired from multiple scans along a scan direction. Therefore, one image is obtained from one scan; N images are obtained from N times of scan. The time required for acquiring the images of all the slices can be calculated as Equation 1 (Eq. 1).
Time required for acquiring the images of all the slices=NEX×Npe×TR×Nslice,  (Eq. 1)
Where NEX denotes the average number of repeated signaling of a single slice, and Npe is the whole number of encoding. For the 2D MR image, Npe denotes the number of phase encoding Np (scan lines in the k-space), TR denotes the time required for acquiring a scan line in the k-space, and Nslice denotes the number of the slices. For example, if there are on the total 256 128×128 images to be acquired, and Nslice=256, NEX=1, Npe=128, TR=0.1 second, then the time required for acquiring the images of all the slices is about 54 minutes. This is indeed a time-consuming procedure.
Referring to FIG. 2, in a conventional procedure of 3D spatial encoding, in one scan only one single slab of the subject can be excited to give the images of all the slices. Also, the time required for acquiring the 3D MR image is calculated as Eqn. 1, but the whole number of encoding Npe=Np×Nz, wherein Np is the number of phase encoding and NZ is the number of phase encoding. Thus, it is apparent that more time is required for acquiring the 3D MR images.
Previous application (US Publication No. 20090278538) discloses a novel method and apparatus for simultaneously acquiring multiple slices/slabs in magnetic resonance system. The method comprises the following steps: applying one or more than one RF pulse, which carries at least two frequency components, and a slice/slab selection magnetic field gradient so that at least two slices/slabs of the subject respectively corresponding to the at least two frequency components can be excited simultaneously; applying spatial encoding magnetic field gradients; and applying a slice/slab separation magnetic field gradient so as to separate the at least two slices/slabs. The method according to the previous invention can be used to acquire data for simultaneously reconstructing multiple slices/slabs.
However, the applied spatial encoding magnetic field gradients and spatial encoding gradients generate a sin c filtering effect in the received signals and destroy high frequency component thereof, as a result, the images acquired by said method are blurry.
Therefore, how to modify the current method and apparatus for simultaneously acquiring multiple slices/slabs in magnetic resonance system as a method and an apparatus which can make the acquired images more clear has become an imminent task for the industries.